Not applicable.
The present invention relates to steering systems for wheeled vehicles, particularly road or all terrain vehicles with at least two steerable wheels under manual control of a driver using lever steering and in which at least the steerable wheels are independently suspended from the vehicle body frame.
The structure, adjustment, and alignment of the steering mechanism of a wheeled vehicle is a somewhat complicated matter involving various relationships of each steerable wheel axle to the vehicle body referred to as caster, camber, toe-in, Ackerman angle and the like. No attempt is made here to present a detailed discussion of all these factors, except as they relate to the improvements of the present invention.
For over a century, the steering system for automotive vehicles has utilized a front axle which does not rotate about a vertical axis when the vehicle is steered to the right or the left. Rather, each front wheel is provided with a stub axle which is rotatable about a vertically disposed king-pin or equivalent pivotal mounting structure. Accordingly, it is necessary to provide means by which the front wheels turn to the left or turn to the right together in a coordinated fashion. It was long ago determined that optimum steering was not achieved with strictly parallel motion of the front wheels because the outwardly turning wheel is closer to the vehicle turning center than the inwardly turning wheel and needs to rotate through a greater angle. This refinement and provision for steering control is referred to as the Ackerman angle provision.
A common and conventional wheeled vehicle steering system provides for the rotation of the steering column or steering shaft to be converted into linear motion of a link which imparts a rotating motion to the stub axle of a wheel through a steering control arm extending from the stub axle. The common means for providing coordinated motion of the two steerable wheels includes a track arm which is fixed with respect to the stub axle on each wheel together with a track rod extending between the two track arms so that the two front wheels are constrained to move (track) in a predetermined relationship either to the right or to the left. In most cases, the linkage provided does not maintain the wheels parallel but rather provides respective non-linear turning relationships which take into account the Ackerman angle provision. As mentioned above, the present invention eliminates reliance upon a track rod or other direct mechanical linkage between the left and right steerable wheels by causing the turning motion of each wheel to be effected by its own independent (left or right) steering motion controller link.
Steering systems for wheeled vehicles have been proposed in prior patents which employ independent right and left steering motion controllers, in the form of hydraulic cylinders, for example, but such known steering systems have commonly provided direct wheel coordination with track rods or equivalent means between the left side and the right side wheel.
U.S. Pat. No. 5,094,312 to Hakel dated Mar. 10, 1992 shows a vehicle steering system in which the left and right steering control arms for the front wheels are both operated by a single double-acting hydraulic piston with oppositely directed piston rods each coupled by a mechanical link to a respective steering control arm. This single piston arrangement is in effect a direct mechanical linkage from the left side wheel to the right side wheel (there are not two independent hydraulic cylinders for the respective left and right steerable wheels). U.S. Pat. No. 4,986,387 to Thompson, et al., dated Jan. 2, 1991 shows a steerable wheeled vehicle with a steerable wheel for which turning motion is provided by hydraulic cylinder and a rack and pinion, but, since there is only one steerable wheel, it provides no teaching with respect to coordination of two steerable wheels relevant to the present invention.
U.S. Pat. No. 5,090,512 to Mullet, et al., dated Feb. 25, 1992 relies on a mechanical connection from a left side cable unit to a right side cable unit of the steering system to produce the non-linear relation for wheel steering; wheel steering angle is directly proportional to cable motion at each wheel. U.S. Pat. No. 4,006,664 to Brown dated Feb. 8, 1977 has hydraulic operated steering, but like the patent to Hakel has only a single cylinder for left and right wheels, the coordinated motion of which must be provided by a linkage directly connecting left and right wheels with the single cylinder provided for their operation.
A cable-type steering device is shown in U.S. Pat. No. 5,893,426 to Shimizu, et al., dated Apr. 13, 1999 wherein flexible push-pull cables from a steering wheel control a power steering motor and a track bar which interconnects both front wheels.
U.S. Pat. No. 2,757,014 to Schmitz dated Jul. 31, 1956 discloses a steering system for a tractor having pairs of control cylinders and operating cylinders for providing steering motion to the respective front wheels which is independently controlled, there being no tie-rod connecting to the two front wheels. Although the independent control of the two front wheels is arranged so that there is a non-linear relationship between the steering motion of the left wheel and the right wheel, this non-linear relationship is not for the purpose of providing a desired Ackerman angle relationship in the steering mechanism, but, rather, is to facilitate very sharp turning of the tractor vehicle about either the left rear wheel or the right rear wheel. Accordingly, the stated objective of the steering system is solely to arrive at an extreme or limit position for the wheels in which the left wheel is turned by ninety degrees and the right wheel is turned by about fifty degrees (or vice versa). No Ackerman angle is sought or achieved for modest steering movement motions and, as the description states, any normal steering movement of the wheel 24 will be transmitted to the wheels 13 and 14 equally. Other features of the Schmitz disclosure make it unsuitable for an all-terrain vehicle or road vehicle; note that the front wheels of the vehicle are not independently suspended and there is no suggestion that it could be modified for inclusion in a vehicle with independent suspension for the steerable wheels.
U.S. Pat. No. 5,931,244 to Renfroe, et al., dated Aug. 1, 1999 discloses a cable steering system which does not include the structure and function of the simple conventional steerable wheel control arm, and uses a complex actuator for each steerable wheel; the U.S. Pat. No. 5,931,244 disclosure also requires that the Ackerman angle relation for wheel angles be provided without contribution from a control arm and its associated linkage. Some general considerations regarding lever steering from the U.S. Pat. No. 5,931,244 patent are applicable here and that patent accordingly is incorporated by reference.
The steering system of the present invention provides lever steering which eliminates the necessity of a steering wheel. The control of the vehicle may be accomplished with either hand or both hands. The double handle configuration of the preferred embodiment gives the operator a sense similar to using motorcycle handle bars except the center section of the handle bars is not present and the levers pivot more fore and aft. This also allows entry and exit to the vehicle through the front of the vehicle if desired, and it removes the danger of the steering wheel and the necessary support structure upon which a person may be injured and impaled in the event of accidents. This then allows increased ride-down distance which can be incorporated into the vehicle restraint system to reduce injuries.
By the present invention, the necessary forces for causing each of the steerable wheels to properly respond to the steering control provided by the driver is effectuated between the vehicle body and each (usually independently suspended) steerable wheel control arm by a steering motion controller and motion displacement transferring elements, preferably in the form of two fore and aft rigid steering links. The coordination of the left wheel and right wheel motion is attained, not with the usual mechanical link between steering control arms for the wheels, but rather by steering motion displacements transmitted to the actuators and to the wheels from the corresponding steering lever. These motions imparted to the wheels by the respective actuators have a predetermined non-linear relation, preferably produced by a non-linear coupling of the actuators and control arms combined. An advantage of the system of the invention is that the necessity for a conventional steering column is eliminated along with the safety hazard that such columns present for the driver in the event of a mishap. Another advantage is that it facilitates a very large vertical travel for the independent suspension. This is especially appropriate when each suspension arm pivots about an axis at least somewhat crosswise of the vehicle (as in U.S. Pat. No. 5,931,244).
The Ackerman steering in the preferred embodiment is accomplished with the angular relationships of a steering motion displacement link, control arm, and steering pivot. The customary lever linkage to convert linear motion to rotational motion of the wheel about the vertical king pin pivot axis is preferably modified for receiving fore and aft motion displacement rather than right-left displacement from the track. The designer is free to set parameters of these wheel steering elements to optimize suspension travel and to prevent bump steer. As another option, one may replace the rigid links structure with a flexible cable linkage performing the same or essentially the same functions. Cables could extend fore and aft to each wheel.
In addition to providing the features and advantages described above, it is an object of the present invention to provide a wheeled vehicle steering system which achieves coordination between the steering motion of the left and right wheels by providing independently actuated steering motion transmitting elements to each of the wheels, the motions of which are coordinated through the mechanical systems thereof, thereby avoiding the necessity of a track bar or other mechanical linkage extending between the right side and left side wheels of the vehicle while providing advantages of lever steering.